Electronic relay



May 1949- E. McDOWELL ETAL 2,471,334

ELECTRONIC RELAY Filed Dec. 9, 1944 I/l Y Ihventor-s: Earle B. McDowell, Pieter JucHbeT,

)MZH Their Attorney.

Patented May 31, 1949 ELECTRONIC RELAY Earle B; McDowell and Pieter Juchter,Scotla, N. Y., assignors to General Electric Company,

a corporation of New York Application December 9, 1944, Serial No. 567,513 Claims. (Cl. 175-320) Our invention relates to electronic relay circuits, and more particularly to improved time delay relay circuits of this type.

- Many electronic time delay circuits have been employed for various industrial applications. It is an object of our invention to provide an improved circuit of this type .which is simple, which does not require that the initiating contacts carry substantial current, and which may be employed Where the circuit of the initiating contacts includes substantial resistance.

It is another object of our invention to provide an improved time delay circuit having one sequence of energization of the load circuit for each closing and opening of the initiating switch which is readily converted to a diiierent sequence of operation.

It is still another object of our invention to provide a new and improved electronic time delay circuit in which the timing circuit is modified in response to a timing operation.

For a better understanding of our invention,

reference may be had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing, Fig. 1 is a schematic representation of one embodiment of our invention; Fig. 2 is a schematic representation of a modification; and Fig. 3 is a schematic representation of still another modification.

Referring now to the drawing, a load circuit I, such as the operating coil of an electromagnetic relay 2, is energized from a source of alternating current provided by the secondary winding 3 of a transformer 4 through the anodecathode circuit of an electric valve 5, which is preferably of the high vacuum type. As illustrated, the valve includes an envelope enclosing an anode 6, a cathode l and a control member or grid 8. The primary winding 9 of the transformer 4 is energized from an alternating current circuit 10. A capacitor l I is preferably connected across the operating coil I of the electromagnet to smooth out the energization of the coil. The relay 2 may be provided with contacts to control any desired number of circuits and, as illustrated, includes normally open contacts [2 and normally closed contacts l3 for controlling circuits l4 and:

I5, respectively.

The conductivity of the electric valve 5 is controlled by the operation of an initiating switch illustrated schematically as a push button It. It will be readily understood that the initiating switch may be provided by the contacts of any suitable instrument such as a level indicator or thickness gauge, for example. The control member 8 is connected with the cathode I through a circuit including a resistor ll, the contacts of the initiating switch l6, 9. switch l8 and a resistor I!) which provides a source of negative bias for the control member 8. The resistor I9 is connected in parallel with a capacitor 28 and in series with the anode-cathode circuit of an electric valve 2! and a winding 22 on the transformer 4. As will be readily understood, the circuit including winding 22 and valve 2| provides a rectifier circuit for producing a negative bias across resistor IS. The circuit of the control member 8 also includes a capacitor 23 permanently connected between the control grid 8 and the cathode 1. Connected in parallel with capacitor 23 is a resistor 24 and a switch 25. As will be described in detail later, switches l8 and 25 are not normally operated in the operation of the relay but are provided to change the circuit connections to provide a different time delay circuit having a diiferent sequence of energization of the load circuit for each operation of the initiating switch l6.

The operation of the embodiment of our invention described above is as follows: With the transformer 4 energized and the initiating switch It open, the control member 8 is maintained at cathode potential by the direct connection of resistor 24 between the cathode and control member. Under these conditions, electric valve 5 conducts current to energize electromagnetic relay 2 andoperate contacts l2 and 13. Upon closure of the initiating switch l6 the negative bias of resistor 19 is impressed on the control grid 8 through resistor H, the circuit being completed through capacitor 23. By making resistor ll small the control grid assumes a negative potential substantially instantaneously and conduction by electric valve 5 is prevented or reduced to such a low value that control relay 2 is deenergized. Upon opening of the switch (6 the control grid 8 remains sufiiciently negative to prevent relay 2 from picking up for an interval determined by the magnitude of resistor 24 which provides a discharge path for capacitor 23. Thus the system of Fig. 1 as described above with resistance I1 and the contact resistance relatively small and resistance 24 relatively large provides for substantially instantaneous deenerglzation of relay 2 upon closure of contact IB and for energization of the relay with a time delay after opening of the switch l6.

If switches l8 and 25 are moved upwardly, as

viewed in Fig. 1, to engage contacts 26 and 27, respectively, it will be noted that the negative bias of resistor 59 is permanently connected to the circuit of the control member through resistance 2t, and initiating switch it is connected in series with resistor H and across the control member to the cathode circuit of the electric valve. With this arrangement it will be apparent that the control member 8 is normally maintained at a substantially negative voltage to maintain the relay 2 deenergized. Upon closure of the initiating switch it, capacitor 23 discharges rapidly through the relatively small resistor i? to energize the load circuit substantially instantaneously upon closure of the initiating switch. Upon opening of the initiating switch it, capacitor 23 charges to a negative value through the relatively large resistor M to again render the valve nonconducting but with a time delay. Thus the circuit as illustrated in Fig. 1 may be readily converted to a difierent circuit having a different sequence of energization and deenergization of the relay for each operation of the initiating switch it.

In some installations it is undesirable or impractical to maintain the resistance ill in the imitating circuit low. For example, in liquid level control systems the circuit ofthe probes employed as contact makers may have considerable resistance. While this resistance is desirable in many applicatons and may serve a useful purpose in limiting current flow through delicate initiating contacts it may operate with the timing capacitor to produce an unwanted delay in the sequence of operation of the control relay. In

the arrangement of Fig. 1, for example, if resistor ll or the contact resistance is of appreciable magnitude there will be a delay in the dropping out of relay 2 upon closure of initiating switch it, as well as a delay in the energization of relay 2 upon opening of contact It.

In Fig. 2 of the drawing we have shown a circuit arrangement which is very similar to the circuit of Fig. 1, with an additional set of normally open and normally closed contacts on the relay 2 for controlling the circuit of capacitor 23. In Fig. 2, those parts corresponding to the parts of Fig. 1 have been designated by corresponding reference numerals. In Fig. 2 in addition to the external circuit controlling contacts it and i5 the relay 2 is provided with a normally open contact 28 and a normally closed contact 29. lIhe normally open contact 28, when closed, connects the capacitor 23 between the cathode and grid of the electric discharge device 5 in the same manner as it is connected in Fig. l, and the normally closed contact 29 establishes a shunt circuit across capacitor 23 for discharging the capacitor.-

In the operation of the modification shown in Fig. 2, the control member 8 of the electric valve 5 is normally connected with the cathode through resistor 26 so that electric valve 5 is conducting and the coil i of relay 2 is energized, contact 28 is closed, and contact 29 is open. This establishes a circuit for capacitor 23 in the grid circuit in parallel with resistor 24. When the initiating switch 16 is closed, the negative voltage appearing across resistor I9 is impressed on the circuit of the control member through resistance H which has been used to illustrate the total resistance in the initiating circuit. With the relay 2 energized, the capacitor 23 draws current through the resistor i! and delays the application of the negative voltage to the control member of valve 5 so that the relay is deenergized with a. time delay. However, when relay 2 drops out, it disconnects the capacitor 23 and establishes a discharge circuit for the capacitor through contact 29 so that upon opening of the initiatng circuit the control member of electric valve '5 immediatelyassumes the potential of the cathode and the relay is picked up immediately.

In Fig. 3 is shown a similar circuit arrangement in which the controlling contacts and capacitor are arranged to drop out the relay immediately upon closing of the initiating switch, and to pick up the relay with a time dela upon opening of the intiating switch. In Fig. 3 the relay has been shown as energized from a direct current supply circuit. Referring now toFig. 3, the relay is energized from a direct current supply circuit 30 instead of the alternating current supply circuit I t. The anode-cathode voltage for the electric valve and the negative bias for the control member thereof, corresponding to the bias produced across resistor i9 of Fig. 1, is provided by voltage resistors 3i and 32, respectively, which are connected in series across direct current supply circuit 30. Resistor 32 is preferably provided with an adjustable tap 33 for adjusting the magnitude of the bias voltage. In the arrangement of Fig. 3, the contacts in circuit with capacitor 23 have been arranged so that when the,

relay 2 is energized, the terminal of capacitor 23 remote from the cathode of electric valve 5 is connected to the source of negative bias voltage. As illustrated in the drawing, this is accomplished by a normally open contact 34 of relay 2 and a conductor 35. A normally closed contact 36 of relay 2 is provided for connecting this terminal of the capacitor directly to the control member when the relay 2 is deenergized. With this circuit arrangement, it is apparent that electric valve 5 conducts and relay 2 is energized before initiating contact i6 is closed. Upon closure of the initiating switch it, the negative voltage is immediately impressed on the control member through the resistor H to deenergize the relay immediately. This closes contact 36 and opens contact 34 and places the negatively charged capacitor across the grid-to-cathode circuit. When contact I6 is opened, the voltage of the grid rises at a rate determined by the discharge of capacitor 23 through resistor 24. Thus the delay that might otherwise result 'from charging capacitor 23 through resistor I1 is eliminated and immediate drop-out of the relay is accomplished upon closure of the initiating switch I6 While energization of the relay upon opening of the initiating switch is accomplished with a time delay.

In the specification and in the appended claims, permanently connected is employed to distinguish from circuits which are normally opened and closed during operation of the device and is applied, for example; to the circuit including switch 25 which may be operated to provide a different circuit but which is not intended to be operated during operation of the circuit originally established.

While we have shown and described a particular embodiment of our invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from our invention in its broader aspects, and we, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a supply circuit, an electromagnetic relay including an operating coil, an electric valve including an anode, a cathode and a control electrode means connecting said supply circuit, the operating coil oi said relay and the anode-cathode circuit oi said valve in seriesra resistor connected between said cathode and control electrode, a capacitor, a source of direct voltage, electrical connections from said source for supplying a charge to said capacitor, a circuit controlled by said relay for connecting said capacitor in parallel with said source of direct voltage when said relay is in one operative position to provide a charge on said capacitor for supplying a negative bias voltage to said control electrode and for establishing a discharge circuit for said capacitor when said relay is in a second operative position, and a circuit including resistance and a normally open initiating contact c0nnecting said direct voltage between said control electrode and said cathode with the negative terminal of said source electrically nearer said control electrode.

2. In combination, a supply circuit, an electro magnetic relay including an operating coil, an electric valve including an anode, a cathode and a control electrode means connecting said supply circuit, the operating coil of said relay and the anode-cathode circuit of said valve in series, a resistor connected between said cathode and control electrode, a capacitor, a source of direct voltage, electrical connections irom said source for supplying a charge to said capacitor, a circuit controlled by said relay for connecting said capacitor in parallel with said source of direct voltage when said relay -is in one operativewosition to provide a charge on said capacitor for supply in: a negative bias to said control electrode and for disconnecting said capacitor when said relay is in a second operative position, and a circuit including a resistance and a normally open initiating contact connecting said direct voltage between said control electrode and said cathode with the negative terminal of said source electrically nearer said control electrode.

3. In combination, a supply circuit, an electromagnetic relay including an operating coil, an electric valve including an anode, a cathode and a control electrode means connecting said supply circuit, the operating coil of said relay and the anode-cathode. circuit of said valve in series, a rsistor connected between said cathode and said control electrode, a capacitor, a source of direct voltage, electrical connections from said source for charging said capacitor, a circuit controlled by said relay for connecting said capacitor in parallel with said source in one operative position v 6 erative position, and a circuit including an initiating contact connecting said direct voltage between said control electrode and said cathode.

first operative position of said relay for precharge ing said capacitor to a predetermined voltage, an initiating switch for controlling the voltage on said control electrode to eflfect operation of said relay to a second operative position, and means responsive to the operation of said relay to said second operative position for connecting said precharged capacitor in circuit with said control electrode to impress a transient negative bias voltage thereon determined by said capacitor and said resistor.

5. In combination, a supply circuit, a relay, an electric valve including an anode, a cathode and a control electrode, means connecting said supply circuit, said relay and the anode-cathode circuit of said valve in series, a resistor connected in the control member-to-cathode circuit of said electric valve, a capacitor, a source of direct voltage, means including connections from said source to said capacitor established in a first operative position of said relay for precharging said capacitor to a predetermined voltage, an initiating switch for controlling the voltage omsaid control elec-- trode to eiiect operation 01 said relay to a second operative position, and means responsive to the operation or said relay to said second operative position for connecting said precharged capacitor in circuit with said control electrode to impress a transient negative bias voltage thereon deterof said relay and in parallel with said resistor to supply a negative bias voltage to said control electrode only when said relay is in a second oplnined by said capacitor and said resistor.

EARLEB. McDOWELL. Pm JUCHTER.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENT! Number 

